This invention pertains to the art of centrifugal fan wheels.
It is well-known in the fan art that centrifugal fan wheels which have blade designs of different types each have their own advantages and disadvantages with respect to the wheels having other types of blade design. Some of the characteristics which vary with blade design include pressure, horsepower, efficiency, noise level, and air delivery rates.
The types of standard centrifugal fan wheels are classified as straight blade, forward curved blade, backward curved blade, radial tip blade, and backward flat blade. Each of these have different characteristics at different air delivery rates which are well-known and have their own characteristic curves.
In some situations it may be desirable to have a single wheel which is adapted to partake of the characteristics of several of the different types of wheels.
It is an aim of my invention to provide a centrifugal fan wheel of a construction which is adapted to have the pitch of its blades changed in order to gain control of airflow substantially independently of the fan speed.